An LED display device is assembled with a plurality of unit LED display screens, so as to form a LED display device having a suitable size according to customer requirements. Each unit (unit) LED display screen comprises a frame, a lamp plate, a control panel, a power supply, and some connectors. The frame is used to support all components of the unit LED display screen. When assembled with unit LED display device screens, as the assembled LED display device may bear not only the whole gravity loading from an upper unit LED display screen, but also an external force from wind loading and a deformation of the frame caused by temperature changes, etc., the frame is required to have a relatively higher strength and better stability to resist a self-pressure and gravity of the unit LED display screen, a tension caused by wind, and a deformation of the frame caused by temperature changes. The lamp plate is formed with a plurality of LED light-emitting units arranged in a dot-matrix. A driving circuit and a system circuit are also arranged on the lamp plate. A lot of heat may be produced during operation of the LED light-emitting units and circuits. If heat cannot be dissipated in time, it may influence the display effect of the LED light-emitting units, and so cause chromatic aberration of the LED light-emitting units, influence display effect of the LED display device, and decrease the life of LED light-emitting units, thus decrease the life of the LED display device.
From the foregoing, with respect to the unit LED display screen, bearing capability of its frame and heat dissipation are two important problems with the LED display screen. At present, the LED display device is commonly designed as a box (box-shaped design) to bear weight and resist external forces, and a fan is arranged inside the box to solve the problem of heat dissipation. However, the box-shaped design has disadvantages of tedious manufacturing process, bigger noise caused by the fan, large volume, heavy weight and inconvenience in assembly and disassembly. CN Patent ZL200920133332.1 discloses a LED display screen using metal aluminum sheet as a thermal conducting module to conduct the thermal energy from the unit LED display screens and driving circuits to air, and as a frame to support the unit LED display screens. Although the aluminum sheet may produce a good heat dissipation effect to solve heat dissipation of the unit LED display screen, temperature may changes during heat dissipation in various operation environments, the aluminum sheet is prone to deformation and does not have enough stability. In addition, due to high density of metals, a substrate made of a metal is heavy, which may cause difficulty in assembly and transportation. Moreover, heavy metal aluminum sheet leads to large gravity of the unit LED display screen on its own, so that it lacks of bearing capability and strength of resisting external forces when a large LED display device is assembled. Therefore, it is urgent to design an LED display device with simple structure, good thermal conductivity, portability, high strength and good stability.